It was huge. Ugly beyond belief. And it would stand in their front yard like a hulking monster throwing its massive shadow across the lawn.

But a group of homeowners said they wanted it. When asked, they said, "Yes."

In the mid-1960s, psychologists Jonathan Freedman and Scott Fraser decided to explore what is often called the "foot-in-the-door" technique  the sales tactic where you start with a small request that is easy to agree to in order to gain acceptance to a much larger request later on.

So, a researcher, posing as a volunteer worker, went door-to-door in a California neighborhood and asked homeowners if they would allow a billboard to be built in their front yards. The homeowners were shown a photograph of the proposed billboard. What they saw was an attractive house almost completely hidden behind a massive sign with amateurish lettering that read DRIVE CAREFULLY.

As you might imagine, few agreed to this absurd request. Only 17%.

However, another group of similar homeowners reacted differently. When the "volunteer" knocked on their door, showed them the picture, and asked to put up this billboard from hell, an overwhelming 76% said, "Yes."

Why the startling difference in response? Two weeks earlier, a different "volunteer" had asked this second group to display a tiny 3-inch sign that read BE A SAFE DRIVER. This request was so small, so reasonable, so easy to agree to, that almost everyone agreed.

And because of that innocent act, because they had agreed to this small request first, they were far more receptive to the enormously larger request two weeks later.

The Rule of Consistency

How can this be explained? Psychologists say it's simple human nature. Specifically, it is a human characteristic called "Consistency."

People are driven to be consistent in all areas of life  in their words, deeds, attitudes, opinions, beliefs, values, habits, and promises. Once a person makes a decision, takes a stand, or performs an action, he or she strives to make all future behavior match this past behavior.

Dieters stick with diet programs they've paid for, even long after it's clear they don't work. College students become fanatically loyal to campus societies after they've gone through difficult and embarrassing hazing. Donors find it difficult to refuse appeals once they've donated to a cause. Consumers stick with brands they've bought before, even if they're more expensive.

Why does the Rule of Consistency work like this? As with every other persuasion principle in this series of articles, Consistency is what psychologists call a "decision heuristic"  a shortcut for making decisions. Life is too complicated to carefully evaluate every element of every situation, so we learn to take shortcuts to help us make what are usually reasonable and reliable decisions.

Consistency is a valuable adaptive behavior. Socially and personally, consistency is beneficial, a practical survival skill in a complex world. Doing things the same way time and time again, or maintaining the same ideas about things, gives us helpful shortcuts.

Consistency makes thinking easy, because there's little thinking needed. Make up your mind about something once, and you never have to think about it ever again. Faced with new situations, you simply recall how you handled it before and the problem is solved. When the Rule of Consistency is triggered, decisions are made almost automatically.

In addition to simplifying our thinking, Consistency also helps us avoid unpleasant emotions. It helps us stick to what we know and avoid the chance of disappointment, embarrassment, failure, and loss.

Moreover, people are not only driven to "be" consistent, but are also driven to "appear to be" consistent. That's because, socially, consistency is a desirable personal trait. It is seen as rational, trustworthy, stable, and decisive. Inconsistency, on the other hand, is usually frowned upon. It is seen as irrational, deceptive, unstable, and indecisive.

Think about the people you most admire. Aren't most of them remarkably "consistent" in their actions and beliefs? Don't they seem incredibly decisive and sure?

Commitment: The Secret of Consistency

Okay, so how do we use this knowledge? How do we trigger the Rule of Consistency?

Let's go back to the billboard experiment for a moment. To explain the massive favorable response of the second group of homeowners, who had first agreed to a small request and then later to a large request, the researchers said:

"What may occur is a change in the person's feelings about getting involved or taking action. Once he has agreed to a request, his attitude may change, he may become, in his own eyes, the kind of person who does this sort of thing, who agrees to requests made by strangers, who takes action on things he believes in, who cooperates with good causes."

Commitment, then, is the key to triggering the Rule of Consistency. Simply put, if you can get someone to make a commitment, even a seemingly inconsequential one, you automatically trigger the Rule of Consistency, which can then help trigger the "yes" response for later, and much larger, requests.

According to Dr. Robert B. Cialdini, the psychologist and author responsible for collating most of the research I'm using in this series of articles, "Once we have made a choice or taken a stand, we will encounter personal and interpersonal pressures to behave consistently with that commitment. Those pressures will cause us to respond in ways that justify our earlier decision."

In fact, he goes on to say, "You can use small commitments to manipulate a person's self-image; you can use them to turn citizens into 'public servants,' prospects into 'customers' ... And once you've got a man's self-image where you want it, he should comply naturally with a whole range of your requests that are consistent with this view of himself."

Can these ideas actually work in the marketplace? Absolutely.

In one trial, The American Cancer Society surveyed people by phone. They asked prospects to predict what they would say if asked to volunteer for three hours to collect donations. Many said they would say, "Yes." Later these people were called again and actually asked to volunteer for three hours. The result? A 700% increase in volunteers. By answering "yes" the first time  to an innocent question  those people took a stand, made a commitment, and later felt compelled to make their actions consistent with their words.

In another test in my home city of Columbus, Ohio, a similar tactic was used to increase voter turnout for a presidential election. Prospects were asked by phone if they would vote on Election Day. For those called, answering "yes" to this simple inquiry increased turnout significantly. Those people went on record about an issue and later were driven to act in a manner consistent with their earlier verbal commitment.

Putting the Rule of Consistency to Work

Now the brass tacks. To get a "yes" response with the Rule of Consistency, follow these suggestions:

1. Start small and build. The "foot-in-the-door" technique works. Begin by asking your prospect to agree to a simple request or a small transaction. Agree to complete a questionnaire or answer questions in a survey. Request information. Sample a product. Say "yes" to a simple question, such as "How are you feeling today?" Anything. By getting your prospect to make a decision, take a stand, or perform an action, you establish a new psychological "commitment."

Once you have that commitment, no matter how small, you will have changed your prospect's self-image just enough to trigger the Rule of Consistency. Since the rule states that people strive to be consistent, you can build on this new self-image and make ever increasing requests. Accepting a free sample can lead to accepting a small transaction. A small transaction can lead to a larger transaction. And so on.

A personal example of how a small commitment can create a powerful new self-image is my decision to go white water rafting last summer. Per the Rule of Consistency, I now think of myself as a "white water rafter" and tell people that one of my interests is rafting. I even subscribe to an outdoor magazine. And I only went rafting one time!

2. Build on existing commitments. In addition to establishing new commitments, you can also build on commitments your prospects have already made. Using your sales message to build on existing commitments guarantees that you will invoke the Rule of Consistency.

For example, if you're selling books on tape and you know your prospects are book buyers, you have a ready-made commitment to build on. Your prospects read and think of themselves as readers. You can then position your product not as the antithesis of reading  which is how many readers see books on tape  but as an extension of efficient reading. "There's no substitute for real books. But as a smart reader, you know you have to prioritize your reading. Now you can enjoy many of the books you just don't have time for in your normal reading schedule."

Get people to take a stand on what they honestly agree with now. Align your product with your prospect's current sense of consistency. "If you're the kind of person who loves fine wine, this magazine was written especially for you."

You can also show that refusing your offer would be inconsistent. "No true wine connoisseur would ever be without the exclusive information this magazine gives you."

3. Get prospects and customers involved and keep them involved. We judge people more by their actions than their words. And people judge themselves the same way. Therefore, action is the key to effective commitments. The more active a commitment, the better.

Instead of having your prospect think something, get them to say it out loud. Instead of saying it, get them to write it. Instead of writing it, get them to do it.

Your requests should not be difficult, just "active," requiring some involvement. Involvement creates inner pressure to adjust the self-image to match the action. And it creates outside or social pressure to adjust the self-image to how others see us.

Involve people with your offers, with your company, with information about your products and services. Let them try samples. Get them thinking about current trends. Make it easy for them to make decisions and take stands.

4. When appropriate, make commitments effortful. Ease of response is always important, but sometimes it's good to make people work a little. Effort increases the power of commitments. The more work someone does to get something, the more committed they are to it and the more likely the Rule of Consistency will kick in.

One form of action that is particularly effective is writing. Writing takes effort, and is more likely to influence behavior than speaking or thinking. People believe that what you write is what you believe, so there's a pull to adjust one's actions and thoughts to what is written.

For example, carpet salespeople often ask customers to fill out their own order forms because this extra effort can boost the commitment to a sale and cut down on the number of cancellations. Customers who provide written testimonials and go on record as liking a product or service are almost always the best customers later on. And tests, quizzes, and applications can make getting into a correspondence course, for example, appear more valuable because of the extra work necessary to be accepted.

5. When appropriate, make commitments public. Commitments can be private, but public commitments create more lasting change. The more public, the stronger the sense of consistency and the less likely a prospect or customer will change later on. Remember, people are not only driven to be consistent, but also to "appear to be" consistent as well.

Find ways to make involvement public when it is appropriate. Get them to write testimonials. Have them fill out forms. Make them members of a special group. Give them certificates and awards. Publish their names in honor rolls. It doesn't have to actually be public, but must "feel" public.

6. Try to attract customers with offers directly related to your product or service. Freebies, premiums, awards, contests, and other motivators usually pump up response, but at what cost? If prospects feel they tried your product or service because of a gift they wanted, they will feel no commitment and will not feel driven to be consistent.

When you get response with offers that are directly related to your product or service, prospects and customers will take "personal possession" of their behavior. It will be an inner choice  a true commitment. Prospects should think, "I responded because this offer looked interesting to me. This is the kind of product someone like me would use."

If you're selling a software program and you offer a free phone card with every purchase, you'll get a lot of buyers who were motivated by the phone card, but aren't prime prospects for most of your products. Offering a free mouse pad or add-on program would be more relevant.

7. Practice "Commitment Management." For every message, you must consider the current state of your prospect's or customer's commitments. Ask yourself: Is there a commitment I must create to sell this? Is there an existing commitment I can use to my benefit? Is there a commitment I need to break? What should the perceived level of commitment be to my first request? My second request?

For example, in reviewing a sponsorship acquisition package for a children's charity, I felt that the current control made prospects feel too committed too soon. I wanted to lower the perceived level of commitment upfront to increase inquiries. Then, in a follow-up package, after prospects had "taken a stand" for helping a child, I wanted to increase the pressure and raise the perceived level of commitment to increase conversions. It worked. My test package produced 35% more inquiries and 20% lower cost per sponsor on conversion.